28 June 2010
New images of spillway at Attabad
Posted by Dave Petley
Unfortunately I cannot access images from Attabad at the moment, but the Pamir Times has this morning published a set that are well worth a look. The images are here. Interestingly, they also note that the water level has reduced by 13 inches (about 33 cm) over the last two days, which is a promising sign. Unfortunately I cannot validate these figures at the moment.
The images seem to show that the key constraint remains the point of the large boulder as before, although the water has now eroded around this, leaving it stranded in the middle of the channel:
The channel is clearly widening on both sides through slope failures, increasing the capacity of the channel, but there is still remarkably little sign of down-cutting. Meanwhile downstream, the dam is continuing to lose mass through erosion, a process that we must watch carefully:
This loss of volume is very slowly weakening the barrier. There are no signs at the moment that this is a cause for real concern, but close monitoring is needed as the flow rate increases.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
http://www.youtube.com/watch?v=QYxj7SmZAA0 This video is more recent and more relevant than the images of pamirtimes. Dave, can you please comment on it?Looks like the boulder in the channel is gone and back erosion is finally coming closish to the saddle!Best RegardsIvan
Ivan- I think the boulder is still there, but the water level is higher, and/or the flow rate is greater, so the water has over topped it. It does appear to be a barrier limiting flow.It would be useful to know the exact date and time the video and the photographs were taken. I suspect the video is more recent, but it I can't be 100% certain.
The boulder sticking straight up does not appear to me to be the principal obstruction of the total flow. Note the smooth nonturbulent flow up to the boulder. This shows that there is little dissipation of kinetic energy. At the upstream side of the boulder the water curls up to about the height of the boulder. The difference between water heights at the up- and down-stream sides of that boulder is a rough measure of the drop from lake level to that point. At the left (near) side we see a drop over a ledge/slab about 1/4 to 1/3 the height of the boulder yielding a drop above the boulder some 3/4 to 2/3 the height of the boulder.Remember that this boulder was originally part of a massive slab leaning on the right (far) band that fractured as it was undermined. I originally thought that this upright slab was the somewhat finger of the massive slab, but these photos show something that rotated up or downstream as it departed its parent slab — a large piece of which I suspect lies immediately upstream.George
Dave- It is apparently "obvious" that this boulder or that boulder is holding back so much water flow.From that same set take a look at this one:http://pamirtimes.files.wordpress.com/2010/06/dsc03368-copy.jpgHow much water is that boulder holding back?
Tropical- I think the boulder in the image you linked to is the one farther down the channel (about 1/2 way from the top down to the former seepage point). Thus, this one isn't affecting things. Perhaps you meant image http://pamirtimes.files.wordpress.com/2010/06/dsc03383-copy.jpgwhich does show what I think is a major impediment to overall volume.In the video, which I think was taken later and at a time when the flow was substantially higher, the water is over topping this boulder, but clearly the video shows it is holding up the water above it. But it is hard to tell whether it is moving, or whether the difference is merely due to the increased water level.
Until the lake level comes down to that boulder, none at all. The obstacles at the sill govern flow and height. George
Divalent-I posted the correct link.The basic claim is that a rock sticking up in the middle of the flow impedes rate of spillway flow. What we need to make sure of is that this is indeed true.The rock that's far below the saddle probably does not affect the flow. I suppose I should support this claim. I hope it is clear that rocks at the bottom of a waterfall do not impede the flow above.On the other hand, in closed hydraulic systems, the entire system, beginning to end, should be considered. A restriction at the end impacts the entire system. It's similar for series electrical circuits.In the example being presented, the inflow versus outflow is critical. In a closed hydraulic system, such as one that's on construction equipment, the inflow and the outflow are equal. The Hunza is not a closed system, so the inflow and outflow are basically never equal (excluding the crossing points).I hope we can agree that the lower elevation rock does not slow the flow rate down–at least not enough to be worthy of further discussion. On the other hand, a rock that creates a so-called "bottleneck" would be significant, but we need to make sure that a rock is creating a significant bottleneck. If the restriction is far enough downstream, then the impact is minimal.Is Dr. Dave's rock close enough to the saddle to create a bottleneck affect? Or, as it appears to myself, is it far enough downstream that the impact is minimal?Unfortunately the rock is presented as an obvious restriction on the spillway flow, but it is not entirely obvious.There is a V before the boulder, and the water is a bit white (my whitewater vocabulary is limited). The saddle is above the Dr. Dave's rock, and way above the rock I used as a counter example.Now we can play the game of impact. Let's start at the saddle and move the restriction downstream. How far until the impact is minimal? If the restriction was on the saddle, a bottleneck would be created. If the restriction was at the base of the dam, no restriction in flow would be present. There's a point where the restriction in flow becomes significant, but it is not clear that it's before or after the actual placement Dr. Dave's rock.Ideally we'd go airlift that one boulder and measure the difference in flow. I wonder what the difference in flow rates would be! How much more would flow without the rock in place?While it is not obvious, at least to myself, that Dr. Dave's rock is creating a significant flow restriction, I could be wrong. Maybe removing the rock would significantly increase flow? I am not sure. While I tend toward the rock being low enough in elevation that it's not a significant restriction, I am not confident of that either. In summary, while I tend toward the rock not being a significant restriction, I am not sure. I don't view it as completely obvious one way or the other.
I think this is the same higher elevation rock:http://pamirtimes.files.wordpress.com/2010/06/dsc03400-copy.jpgThe spillway increases in width, if I am reading the photo correctly. We do know that the total volume of water passing the width is the same at this point as further up the spillway, but what is not obvious is the cross sectional area. The water flow in the lake is very slow because the lake has a large cross sectional area. The water flow in a bottleneck is fast, given the smaller cross sectional area.At the same time, when water loses elevation, it speeds up.It appears that we have a loss of elevation as well as a widening of the channel. I'm guessing, and this is only a guess, that the cross sectional area is also greater where the rock is (use the minimum 'transverse' area–where transverse is assumes a linear flow), versus the saddle, bottleneck area.Maybe to the trained eye it is 100% obvious that the boulder is definitely, without question, impacting the total flow.
Below the second midstream boulder down the spillway, there seems to be a transition in gradient. The recent photos show three ledges/slabs at this point that I suspect have halted the retrogressive erosion. The right bank shows a number of slabs, mostly pale yellow in this section; however the two prominent midstream boulders are dark grey with light veins.At this point I would be extremely cautions about landing boats on the right bank ramp close to the spillway as one photo shows a distinct crosscurrent that could suck a boat down into the spillway. I have seen exactly that happen similar situation.George
George- Considering the right-hand side is the active slide side, and that the road is on the left-hand side, I would guess that there won't be too many right-hand side landings. If workers or someone wanted to take photos on the right-hand side, then the lake would be a way to cross from one side to the other.
Tropical – Compare image 3386 to 3400, which view the boulder from upstream and downstream, (and compare to 3405) and it is pretty clear the water is stacked up against this rock on the lake side, and is perhaps a meter or so lower on the downstream side. As a first approximation, use Flow = delta-P / R to estimate the relative resistance here, and it is larger than at any point up to the rock. Yes, it is clear that the channel is trying to erode sideways around it, but (in my non-expert opinion), the problem is that the banks are steep and high here, so it is slow going.I agree the “V” lines above it (particularly on the left side) are another high(er) resistance point, but the level change there is not nearly as significant, and so IMO, isn’t currently a severe limit on flow. I think (again, I’m no expert) that outflow is pretty much going to track lake level until this boulder eventually gets dislodged. I don’t think any other activity will help things, and things like widening the channel above this point may even be counter productive. (I think in general, that given the composition of the material on the bank, you only want that stuff falling into the channel when the velocity is fast enough to remove nearly all of it; otherwise it will only have the effect of clogging the channel at that point.)But, hey, I’m no expert.BTW, two images (3410 and 3403) show the fine work they made of the huge boulder out at the mouth of the channel (the one Dave has images of in his June 22 post), and it is quite clear that, contrary to Dave’s speculation, this was not a test area. Rather, they accomplished two thing: 1) they (rather impressively, I must admit) removed every bit of rock that was above the water line out there (and hence, rock that was not affecting water flow) and 2) those rock chunks now litter the channel bottom, and so are now impeding water flow. I’m not sure why they worked on this, other than perhaps because they could. (I honestly don’t think there was anything they could have done about the key boulder right now.)
Divalent-In 3386 there is a person on the left-hand bank. I use that for a scale approximation.From that, I am going to guess the boulder is about 8 meters.Also in 3386, it appears that the bottleneck is near the standing man. See 3382 also. The man is standing near where the blasted rock was. If someone suggested the bottleneck was about 30 meters downstream from the man, I would consider it reasonable.Let's look at 3400 & 3405.In 3400 it looks like there is about a five meter drop in elevation, plus or minus. I make this approximation based on the rock being 8 meters high, and the river height changes significantly there, including the shift to total whitewater.That said, looking at 3405 reminds me of when I visited the Tacoma Narrows in 2005. I happened to be there during a near maximum tidal flow event. I forget what the speed of the water was. Oh, I guess I should also say that the Tacoma Narrows is definitely, without question, a bottleneck. It would be difficult for me to begin to imagine the peak maximum flow, which is shut off after about 6 hours.Needless to say, the water was riding high up pylons on Narrows Bridge (the replacement to Galloping Gurdy). Admittedly the pylons are in the bottleneck area, but the water is very deep (I'd guess 500-800 feet in the middle area, about 150 feet deep at the pylons).I hope it is safe to suggest that the pylons don't significantly restrict the total flow.Yes, while everyone else was drinking wine and eating cheese, I was looking at the flow rates and water impact on the pylons.Some things that need to be noted, however:1. There is some whitewater on the right-hand side near the start of the spillway.2. There is some whitewater near where the man is standing.The saddle point might be back near the man, and the narrow channel is relatively flat, but sloping down, so the restriction is mainly the width and depth of the channel.It might also be that the saddle point is 30 meters, plus or minus, downstream from the man, but the total flow from the depth and rock placement are such that the whitewater shows up near the shores.I guess we should also define saddle point. If the saddle point occurs in a wide area, it might be less restrictive than a narrow area with bed elevation, which brings us back to this rock.It's tough when all we have is very limited information…
Oh, one more thing:Look at the right-hand elevation drop in 3383. It looks like the right-hand side drops well before the center rock; plus the upstream V is quite obvious.
Let me apologize for not putting these all in one message, but after looking over 3405 some more–My guess is that the center of the spillway is the deepest point until near that boulder. The boulder sticks up, so we know that's not the deepest point in that area. The deep area shifts from the center to the outside edges.Again, let me apologize for the multiple messages that should have been included in a single message.
I can agree that the saddle about 30 m downstream of the man in 3382 governs the flow and level. Note the two V's by the man and 30 m down. Both V's are straddled by eddies. The top of each eddy is just below the downstream edge of an obstruction. Note also that eddies on the side of a V are at a maximum height differential at the top and that this differential decreases towards the bottom of the V. The flat cross-sectional profile at the top of these two Vs indicate a deep bottom. Earlier pictures at low flow were strongly suggestive of underwater slabs at the main V and below, but the recent increased volume obscures these bottom features.It surprises me that the first midstream boulder is still sticking straight up beam on to the current after it dropped into its present position. It may be anchored by a fortuitous slot between horizontal remnants of the parent slab that was earlier leaning on the right bank.My concern about boat landings on the right at present flow levels stems from when the locals from upstream landed there to widen the banks.George
I wish you had seen the site of slide before it happened on 04th of Jan 2010. You would have reached the conclusion that i have reached long ago, that the lake is there to stay without any danger of bursting for a long time to come. Please join me in recommending to covert this disaster to an opportunity – by using it for generating 40 MW in winters and 400Mw for the three months in summers.
Mr Beg are u from pak fauj? nice idea..
According to the account owner ("NorthPakistan") who uploaded the recent video of the spillway (the one that Ivan links to in the very first comment above), that video was shot on June 25th, at about 5 pm.(here's the link again: http://www.youtube.com/watch?v=QYxj7SmZAA0 )So I don't think it can be assumed that this video is more recent than the images over at the Pamir Times. (We don't know when those were taken, but clearly it was after the blasting activity was completed.)
Why can't you access images? Have the authorities knobbled the FOCUS people so they can't give you any information? It seems madness if they have – as the comments section of your various posts show, your blog is by far and away the best source of pure data, information, analysis and reasoned debate of the situation at Attabad.
Brigadier (retired) Hissam Ullah Baig – a former decorated officer, has come up with his typical anti-Wakhi & anti-Gojal suggestion. This is an attempt at ethnic cleansing which the people of Gojal are likely to resist. On technical grounds, the area being seismically vulnerable is not feasible for construction of any mega project. The learned Brigadier, trained as an engineer, seems to be missing the point. The MKT (Main Karakuram Thrust) fault line passes through this region and several off shoots of the main thrust are also crossing the Attabad/Ayeenabad/Shishkat region. Due to increased storage of water volume over the land of Shishkat/Ayeenabad/Gulmit already straining of the fault lines has been reported, expressed through blast-like sounds heard underneath Shishkak. Constructing a water bomb on the head of a country is tantamount to enmity of the state.
Compare 3405 in this last series with pr13 in the June 17th series.pr133405Notice how much has eroded from the right side in the photos. I think that large rock will not be an issue much longer. The spillway is cutting the side opposite from the access road. If downcutting happens there, the lake could start to drain very quickly. full series links June 17 http://pamirtimes.net/2010/06/17/pictory-local-volunteers-efforts-to-widen-the-hunza-lake-spillway/and June 28 http://pamirtimes.net/2010/06/28/deadline-given-by-protesters-for-excavation-of-the-spillway-ends-today/
Yes, the right bank has eroded and the cracks indicate that more erosion will happen. If/when bank erosion works its way around the underlying slabs at the top, downcutting could quickly effect major changes in the situation. It seems that peak flow is a month away at twice the current level; so, there is a distinct probability that this will happen.Hindsight tells me that geologic investigation could have disclosed the slabs in time to have drilled down and broken them up with charges so that the lake could have been discharged at a low flow period. That and sufficient excavation equipment could have spared a large portion of the upstream population and enabled the downstream people to live normally after the lake level was reduced.Of course an earthquake could change the situation in a blink of the eye and reports of fault strains indicate that this may happen sooner than later.George
come on anonymous…. pak fauj is the best..knows everything abt everything… how abt constructing a kargil and siachen victory towers on top of the dam?
http://gbtimes.wordpress.com/2010/06/29/a-lay-man%e2%80%99s-eyes-could-see-the-possibilities-of-expanding-the-spillway-but-expert-of-fwo-could-not-see-these-obvious-possibilities-deadline-of-ten-days-is-over-and-in-ten-day-fwo-could-make/#more-1904 http://pamirtimes.net/2010/06/30/attabad-disaster-a-documentary-by-nisar-ahmed/#comments